Device and method for processing cement kiln combustion exhaust gas

ABSTRACT

A combustion exhaust gas processing device comprises: a dust collector collecting dust in a cement kiln combustion exhaust gas; a wet dust collector as a catalyst-poisoning-substance stripper removing a catalyst-poisoning substance from a combustion exhaust gas which passed the dust collector, preheaters heating beforehand a combustion exhaust gas which passed the wet dust collector; and a catalyst device from which NOx, a persistent organic pollutant, etc. in the preheated combustion exhaust gas, are removed. A titanium-vanadium catalyst etc. as an oxide catalyst is used upstream of the catalyst device, and a platinum catalyst etc. as a noble-metal catalyst downstream of the catalyst device. The temperature of the combustion exhaust gas after the catalyst-poisoning substance is removed is increased up to 140° C. or more with the preheaters to prevent decline in denitration efficiency of and the decomposition efficiency of a volatile organic compound.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 11/794,820, filed on Jan. 14, 2008, which claimspriority to International Application No. PCT/JP2005/23859 which wasfiled on Dec. 27, 2005 and claims priority to Japanese PatentApplication No. 2005-001496 filed Jan. 6, 2005.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH

Not Applicable

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a device and a method for processingcement kiln combustion exhaust gas to remove harmful substances such asdust, NOx, persistent organic pollutants including dioxins, a volatileorganic compound and CO.

2. Background Art

As shown in FIG. 2, a cement burning facility 21 comprises a preheater22, a calciner 23, a cement kiln 24, a clinker cooler 25 and so on, andcement raw meal R, which is fed to the preheater 22 from raw materialsupplying system, is preheated in the preheater 22, calcined in thecalciner 23, burned in the cement kiln 24, and produced clinker iscooled in the clinker cooler 25. Here, the combustion exhaust gas fromthe cement kiln 24 is processed through desulferization in the preheater22 and dust collection using an electric precipitator 26 since limestoneas a main raw material has a property to adsorb SOx, and processedcombustion exhaust gas is discharged in the atmosphere through a fan 27and a stack 28.

Although there was not much harmful substance contained in thecombustion exhaust gas from the cement kiln 24, such as alkali,chlorine, sulfur, and heavy metal and so on, since it is expected, withthe increase in the amount of recycle raw materials and fuels processedby a cement manufacturing facility in recent years and a future increaseplan, that the amount of the harmful substance increases, there is apossibility of becoming a problem from now on.

Then, in order to remove the above-mentioned harmful substances, forexample, a technology is described in the first patent document. Thistechnology comprises the steps of: bleeding a part of combustion exhaustgas from the inlet hood of a cement kiln; supplying cooling air to thebled gas to cool it to 600-800° C.; introducing the cooled exhaust gasinto a cyclone to catch coarse grain dust through separation;introducing the caught coarse grain dust to the kiln inlet hood forcirculation; introducing a part of cyclone exhaust gas to the kiln inlethood to recover heat of the remainder of cyclone exhaust gas; andfeeding the exhaust gas to a dust collector to remove fine grain dust.

Furthermore, for the same object as the above, a technology is describedin the second patent document. This technology comprises the steps of:sampling preheated raw meal introduced to a kiln inlet hood to analyzethe content of harmful substance therein; controlling the amount ofemission that circulates from a cyclone to a kiln inlet hood so that ananalysis result becomes desired value; controlling a cooling air flowrate so that cyclone inlet gas temperature becomes in the range of600-800° C.; and simultaneously detecting the cooling air flow rate andthe amount of the emission, and controlling the amount so that theamount of emission discharged out of a system from the dust collectorbecomes approximately equal to the cooling air flow rate.

Moreover, a technology is described in the third patent document, whichcomprises the steps of: supplying fuel from a fuel-supply opening, andwaste containing ammonium nitrogen from the fuel-supply opening and/orits neighborhood to burn them; and introducing gas containing ammoniainto a part of 700° C. or more in the phase before burning the wastecontaining ammonium nitrogen to reduce the amount of NOx generated andnot to sprinkle offensive odor at the suppression of the NOx.

Furthermore, in the forth patent document, in order to effectivelycollect low-melting compounds from the exhaust gas of cement burningfacility, a method and a device are disclosed, in which a part ofexhaust gas is bled from cement burning facility to collect low-meltingcompounds; then the temperature of the bled exhaust gas is brought to1100-1500° C.; and then the bled exhaust gas is quenched to 120-600° C.to collect the low-melting compounds.

-   Patent document 1: Japanese Patent Publication No. Heisei 11-130489    gazette-   Patent document 2: Japanese Patent Publication No. Heisei 11-130490    gazette-   Patent document 3: Japanese Patent Publication No. 2000-130742    gazette-   Patent document 4: Japanese Patent Publication No. 2003-277106    gazette

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing an embodiment of a combustion-exhaust-gasprocessing device according to the present invention;

FIG. 2 is a flow chart showing an example of a conventional cementburning facility; and

FIG. 3 comprises schematic diagrams for explaining the mesh size of acatalyst (bore diameter of a catalyst) of a honeycomb catalyst, in which(b) is an enlarged view of (a).

BRIEF SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As mentioned above, although harmful substances, such as heavy metaldischarged with the combustion exhaust gas from a cement kiln, do notpose a problem quantitatively until now, various recycle raw materialsand fuels are fed into the cement burning facility in response to therequest of a recycled-resources activity in recent years, and when theinput of recycled resources will continue increasing from now on, theamount of emission of the harmful substances increases, and there is apossibility of becoming a problem. Moreover, since the combustionexhaust gas, which occurs with a cement burning facility is abundant, aclarifying facility of the harmful substances will also becomelarge-scale, and will have a possibility that facility cost andoperating cost may increase.

It is therefore the object of the present invention to provide a deviceand a method for processing combustion exhaust gas which can efficientlyremove the harmful substance in cement kiln combustion exhaust gas,holding down facility cost and operating cost low.

Means for Solving the Problem

To solve the above problem, the present invention is a device forprocessing cement kiln combustion exhaust gas characterized in that thedevice comprises: a dust collector collecting dust in cement kilncombustion exhaust gas; a catalyst-poisoning-substance stripper removinga catalyst-poisoning substance from the cement kiln combustion exhaustgas that passed the dust collector, a preheater heating beforehand thecement kiln combustion exhaust gas that passed thecatalyst-poisoning-substance stripper; and a catalyst device removing atleast one selected from nitrogen oxide, a volatile organic compound,carbon monoxide, a persistent organic pollutant, hydrocarbon and anoffensive odor substance in the cement kiln combustion exhaust gaspreheated by the preheater. Here, the persistent organic pollutants(POPs) are, for example, PCB (polychlorinated biphenyl) and dioxin,which remain in environment by resistance to decompose and affectpeople's health and ecosystem. Further, the hydrocarbon and theoffensive odor substance are saturated aliphatic hydrocarbon,unsaturated aliphatic hydrocarbon and aldehydes, alcohols, ketone, afatty acid group, ester species, a sulfur compound, amines, and othernitrogen compounds, specifically, such as ammonia, methyl mercaptan,hydrogen sulfide, methyl sulfide, methyl disulfides, trimethylamine,acetaldehyde, propionaldehyde, normal butyraldehyde, isobutyraldehyde,normal valeraldehyde, isovaleraldehyde, isobutanol, ethyl acetate,methyl isobutyl ketone, toluene, styrene, xylene, propionic acid, normalbutyric acid, normal valeric acid, isovaleric acid and so on.

With the present invention comprising the steps of: collecting dust incement kiln combustion exhaust gas with a dust collector; removing acatalyst-poisoning substance from the combustion exhaust gas by acatalyst-poisoning-substance stripper; preheating the combustion exhaustgas with a preheater; and removing at least one selected from nitrogenoxide, a volatile organic compound, carbon monoxide, a persistentorganic pollutant, hydrocarbon and an offensive odor substance in thecement kiln combustion exhaust gas, harmful substances can be removedfrom cement kiln combustion exhaust gas without a large-scale facility,and the operating cost for removing harmful substance can also be helddown low.

In the device for processing cement kiln combustion exhaust gas, thecatalyst-poisoning-substance stripper can be a wet dust collector thatremoves a catalyst-poisoning substance from the combustion exhaust gas,preferably a scrubber adding sodium hypochlorite to the cement kilncombustion exhaust gas or a bag filter for which dust is collected whileblowing activated carbon into the cement kiln combustion exhaust gas.With the scrubber adding sodium hypochlorite to the cement kilncombustion exhaust gas, hydrogen chloride as a catalyst-poisoningsubstance is removed with being dissolved in water, dust can becollected with the scrubber, and mercury as a heavy metal can also beremoved efficiently. Moreover, by using the bag filter for which dust iscollected while blowing activated carbon into cement kiln combustionexhaust gas, or the activated carbon filter filled up with activatedcarbon, as a catalyst-poisoning-substance stripper, dust and mercury asa catalyst-poisoning substances can be removed efficiently, and SOx canalso be removed.

In the device for processing cement kiln combustion exhaust gas, theconcentration of the sodium hypochlorite is preferably in a range of 1mg/L or more and 1,000 mg/L or less. When the concentration of thesodium hypochlorite added is less than 1 mg/L, the elimination factor ofcatalyst-poisoning components, such as Hg, Ca, K, and dust, which arecatalyst-poisoning substances, falls, and the coating weight of thecatalyst-poisoning substances increases, resulting in decreaseddurability of the catalyst. On the other hand, even if the concentrationof the added sodium hypochlorite liquid exceeds 1,000 mg/L, theelimination factor of the catalyst-poisoning substances reachessaturation, and the effect beyond this cannot be expected.

In the device for processing cement kiln combustion exhaust gas, thecatalyst device may be provided with an oxide catalyst such as atitanium-vanadium catalyst upstream of the catalyst device, and anoble-metal catalyst having at least one noble metal selected fromplatinum, palladium, rhodium and ruthenium downstream thereof. And, areducing agent is preferably sprayed from an entrance-side upper part ofthe catalyst device.

There is no denying that cement kiln combustion exhaust gas containsharmful substances such as NOx, carbon monoxide, persistent organicpollutants, volatile organic compounds in low concentration but overmany components. In the method of processing the cement kiln exhaust gasusing a catalyst, on the catalyst arrangement in a catalyst device, itis more desirable to arrange an oxidation catalyst upstream and toarrange a noble-metal catalyst downstream rather than to arrange anoble-metal catalyst upstream and to arrange an oxidation catalystdownstream. Treatment of NOx and volatile organic compounds becomeseffective especially by taking the form which sprays NH₃ from theinlet-port upstream part of a catalytic reaction device; arranges anoxidation catalyst in a catalytic reaction device to the upstream; andarranges a noble-metal catalyst to the downstream thereof. By thereverse pattern for the arrangement in a catalyst that a noble-metalcatalyst is arranged upstream, and an oxidation catalyst downstream,while the removal performance of NOx falls, deodorizing performance alsoworsens notably.

Further, the mesh size (bore diameter) of the oxide catalyst, such as atitanium-vanadium catalyst and of the noble-metal catalyst havingplatinum, palladium, rhodium or ruthenium may be 1.75 mm or more and3.75 mm or less, more preferably 1.75 mm or more and 2.90 mm or less.The catalyst-poisoning-substance stripper will remove poisoning mist andpoisoning dust; blinding by the mist and dust of the catalyst will beavoided; and durability will also improve because coating weight of thepoisoning object decreases. With the catalyst of the mesh size (borediameter) of greater than 3.75 mm, although the blinding by mist anddust becomes more difficult to occur, since the contact area of exhaustgas decreases, the amount of required catalysts increases, and itbecomes disadvantageous economically. On the other hand, if the meshsize (bore diameter) of a catalyst is less than 1.75 mm, although thecontact area of exhaust gas will become large, and the amount ofrequired catalysts effectively decreases, the pressure loss of exhaustgas defectively increases, and the poisoning mist and poisoning dustwhich cannot be further removed by a poisoning substance stripper willcome flying, which will become a cause of the blinding of a catalyst,and its durability will also fall.

In the device for processing cement kiln combustion exhaust gas, thepreheater may be a Ljungstrom-type heat exchanger, a heat pump or a heatpipe. With this construction, heat recovery efficiency rises and thefacility cost of this processing device can be reduced substantially.

Further, the present invention is a method for processing cement kilncombustion exhaust gas characterized in that the method comprising thesteps of: collecting dust in cement kiln combustion exhaust gas;removing a catalyst-poisoning substance from the cement kiln combustionexhaust gas of which dust is collected; heating the cement kilncombustion exhaust gas of which catalyst-poisoning substance is removedup to 140° C. or more; and removing with a catalyst at least oneselected from nitrogen oxide, a volatile organic compound, carbonmonoxide, a persistent organic pollutant, hydrocarbon and an offensiveodor substance. In order to prevent decline in denitration efficiencyand the decomposition efficiency of a volatile organic compound, thetemperature of the combustion exhaust gas after the catalyst-poisoningsubstances is removed is increased up to 140° C. or more, and asmentioned above, without a large-scale facility, harmful substance canbe removed from cement kiln combustion exhaust gas, and it becomespossible to suppress the operating cost for removing harmful substanceto low.

In the method for processing cement kiln combustion exhaust gas, inaccordance with concentration of nitrogen oxide in the cement kilncombustion exhaust gas, whether ammonia gas can be added to thecombustion exhaust gas after the catalyst-poisoning substance isremoved, or aqueous ammonia or urea water may be added to the combustionexhaust gas of 140° C. or more and then the combustion exhaust gaspasses the catalyst. With this method, while rationalizing the amount ofthe ammonia used, the amount of the ammonia discharged out of the systemcan be stopped to the minimum.

Further, in the above method, the combustion exhaust gas after thecatalyst-poisoning substances is removed is controlled to be 140° C. ormore using heat recovered from the combustion exhaust gas passed thecatalyst or/and steam generated by remaining heat in a plant with thecement kiln. With this, the combustion exhaust gas from a cement kilncan be processed, using the energy in the plant effectively.

Effect of the Invention

As mentioned above, according to the device and method for processingcement kiln combustion exhaust gas according to the present invention,it becomes possible to efficiently remove harmful substance generatedwith a cement burning facility, holding down facility cost and operatingcost low.

DETAILED DESCRIPTION OF THE INVENTION The Best Mode to Carry Out theInvention

Next, one embodiment of this invention will be explained referring toFIG. 1. As explained in the column of “Background Art”, a cement burningfacility 1 comprises a preheater 2, a calciner 3, a cement kiln 4, aclinker cooler 5 and so on, and cement raw meal R is fed to thepreheater 2 from raw material supplying system not shown, and cementclinker Cl is produced through preheating in the preheater 2, calciningin the calciner 3, burning in the cement kiln 4. The produced clinker Clis cooled in the clinker cooler 5 and is ground in a finishing process.

The combustion exhaust gas processing device according to the presentinvention is disposed downstream of the cement burning facility 1, andcomprises an electrostatic precipitator 6 collecting dust in thecombustion exhaust gas G1 from the preheater 2; a wet dust collector 7which collects water-soluble materials, dust, etc. in the combustionexhaust gas G2 discharged from the electrostatic precipitator 6 andfunctions as a catalyst-poisoning-substance stripper, a sodiumhypochlorite generator 9 which supplies sodium hypochlorite to the wetdust collector 7; a heat exchanger 10 and a heater 11 for heatingbeforehand combustion exhaust gas G3 which passed the wet dust collector7; a catalyst device 12 removing NOx and persistent organic pollutantssuch as dioxin in the preheated combustion exhaust gas G4; asolid-liquid separator 16 which carries out solid-liquid separation ofthe slurry S discharged from the wet dust collector 7; and a mercuryadsorbing tower 17 which adsorbs mercury in the fluid separated by thesolid-liquid separator 16.

The electrostatic precipitator 6 is installed to collect dust in thecombustion exhaust gas G1 from a preheater 2. It is possible to disposea bag filter in place of the electrostatic precipitator 6, and both ofthem can be installed together.

The wet dust collector 7 is installed to collect water-soluble materialsand dust in the combustion exhaust gas G2 which passed the electrostaticprecipitator 6, and the wet dust collector 7 removes dust, sulfuric acidmist, hydrogen chloride (HCl), mercury (Hg), etc as catalyst-poisoningsubstances which have big effect on the life of the latter catalystdevice 12.

Mixing scrubbers (Mu scrubber manufactured by Mu Company Limited etc.)can be used for this wet dust collector 7, for example. Meanwhile, amixing scrubber is characterized by having arranged two or morediffusers in a cylindrical body, and the mixing scrubber gives turningto the flow of gas and fluid, while the gas and fluid move with acountercurrent or concurrent into the cylinder, and is a device tocontact gas and fluid with each other for reaction and dust collection.Preferably, gas and fluid are made concurrent, and the diffusers, whichgive a right wheel to this flow, and the diffusers, which give a leftright wheel to this flow, are arranged by turns. Moreover, in order toavoid that a device is enlarged too much, the residence time of thecombustion exhaust gas of the wet dust collector 7 is set between 1second and 10 seconds.

Under the wet dust collector 7, a circulating liquid tank 7 a isarranged, and a pump 8 is disposed between the wet dust collector 7 andthe circulating liquid tank 7 a, and the slurry generated by the wetdust collector 7 can be circulated through the circulating liquid tank 7a and the pump 8.

The sodium hypochlorite generator 9 is disposed to supply sodiumhypochlorite to the wet dust collector 7, and it oxidizes the mercurycontained in the combustion exhaust gas G2 with the sodium hypochlorite.It is desirable to use an in-line-polarity-transformation type for thesodium hypochlorite generator 9. This type of generator directlyelectrolyzes in treated water without salt water.

The heat exchanger 10 performs the heat exchange of the combustionexhaust gas G3 discharged from the circulating liquid tank 7 a, and thecombustion exhaust gas G5 discharged from the catalyst device 12. It isdesirable to use a Ljungstrom (trademark)-type heat exchanger (made byALSTOM K.K.) for this heat exchanger 10. The Ljungstrom-type heatexchanger heats a heat reservoir directly in heat side gas, and heatedgas is also directly warmed. For example, it is prepared, in the core ofcasing of a body, a disc-shaped heat exchange element pivotallysupported, and the heat exchange element has radially many wave steelplate that are mutually laminated and has a clearance mutually, and aheat exchange is performed by passing the combustion exhaust gas G3discharged from the circulating liquid tank 7 a, and the combustionexhaust gas G5 discharged from the catalyst device 12 in the clearance.

The heater 11 is installed to heat the combustion exhaust gas G4discharged from the heat exchanger 10 using the steam ST generated byremaining heat or the like in the plant in which the cement burningfacility 1 is installed. The reason why the combustion exhaust gas G4 isheated is to more effectively perform denitration and decomposepersistent organic pollutants such as dioxins. Moreover, ammonia (NH₃)used as a NOx reducing agent with the latter catalyst device 12 is addedon the entrance side of the heater 11. The reason why ammonia is addedupstream of catalyst device 12 is to utilize the mixing effect by thefan 14 or the heater 11, and it can be added between the outlet of thewet dust collector 7 and the inlet of the catalyst device 12, where theabove mixing effect is available other than the entrance side of theheater 11.

The catalyst device 12 is installed to decompose and remove NOx andpersistent organic pollutants, etc. in the combustion exhaust gas G4that passed the heat exchanger 10. By forming this catalyst device 12 inthe shape of a honeycomb, even when processing a large amount ofcombustion exhaust gas G4, it can constitute comparatively small.

Next, the catalyst used with the catalyst device 12 is explained indetail. In the catalyst device 12, the catalyst used for the usualexhaust gas treatment can be used, for example, a NOx removal catalystfor exhaust gas can also be used. In the catalyst device 12, atitanium-vanadium catalyst as an oxide catalyst is used upstream, and aplatinum or a palladium catalyst or the like as a noble-metal catalystis used downstream.

A titanium-vanadium catalyst means the catalyst that makes titanium (Ti)and vanadium (V) indispensable. This catalyst exhibits a high functionin decomposition clearance of a volatile organic compound as a harmfulsubstance, while having the high decomposition activity (denitrationactivity) of NOx as a harmful substance.

Furthermore, one or more sorts of metallic oxides selected from tungsten(W), molybdenum (Mo), silicon (Si), zirconia (Zr) can be usedcollectively. Preferably, the independent oxide of Ti, it is using stillmore preferably one or more sorts selected from titanium (Ti), silicon(Si) and zirconia (Zr) of metallic oxides, and two element-systemmultiple oxide of Ti and Si or two element-system multiple oxide of Tiand Zr is especially more desirable.

Although the content in particular of the titanium (Ti) occupied in atitanium-vanadium catalyst is not limited, it is desirable, as an oxidereduced mass ratio to the total mass of a titanium-vanadium catalyst,15-9.9 mass percent, for example, and 30-99 mass percent is moredesirable. Sufficient effect may not be acquired by lowering of aspecific surface area etc. in case of under 15 mass percent, and on theother hand, when 99.9 mass percent is exceeded, there is a possibilitythat sufficient catalytic activity may not be acquired.

Although the rate in particular of at least one sort of metallic oxideschosen from the group which consists of vanadium (V), tungsten (W) andmolybdenum (Mo) is not limited, it is, as an oxide reduced mass ratio tothe total amount of a titanium-vanadium catalyst, 0.5-30 mass percent,and preferably 1-20 mass percent. There will be a possibility thatsufficient catalytic activity may not be acquired as it is under 0.5mass percent, and on the other hand, if 30 mass percent is exceeded,agglomeration of a catalyst component takes place, and while there is apossibility that sufficient performance may not be obtained, the cost ofthe catalyst itself will become high and will lead to the jump ofexhaust-gas-treatment cost.

As a noble-metal catalyst laminated downstream of a titanium-vanadiumcatalyst, an oxidation catalyst with at least one sort of noble metalschosen from platinum, palladium, rhodium and ruthenium and/or thecompound of those is used. This catalyst can use a carrier suitably, forexample, platinum etc. for a carrier, and alumina, silica, zirconia,titania, vanadia, ferrous oxide, manganese oxide, and these mixtures andmultiple oxides can be used as a carrier. Moreover, thetitanium-vanadium catalyst can also be used as a carrier.

The example of preparation of a noble-metal catalyst is shown below. Tothe titanium-vanadium catalyst powder or slurry, the salts of thesenoble metals, or its solution can be added, for example. Moreover,making it impregnated can perform support of at least one sort of noblemetals chosen from platinum, palladium, rhodium and ruthenium and/or itscompound component, and this impregnating support is more desirable.

In a noble-metal catalyst, noble metal and/or its compound to a carrier,as a metal, is 0.001 to 5 mass percent, more preferably 0.05-2.5 masspercent. If it is under 0.001 mass percent, the decomposition activityof a volatile organic compound becomes low, and when it exceeds 5 masspercent, the activity corresponding to the addition is not acquired andnot desirable.

Moreover, in the above-mentioned oxide catalyst and noble-metal catalystwhich are used for the catalyst device 12, alumina, silica, silicaalumina, cordierite, titania, stainless steel, metal, etc. may besupported and used for the carrier of plainer shape, the shape of acorrugated plate, tabular shape, the shape of a net, the shape of ahoneycomb, the shape of a column and cylindrical shape.

As a preparing method of the catalyst, there is no restraint inparticular, for example, conventionally publicly known methods, such asa sedimentation (coprecipitation method), self-possessed method, andkneading method, can be adopted. For example, the binary system multipleoxide containing titanium oxide and one or more sorts chosen fromsilicon (Si) and zirconium (Zr), titanium oxide, or the mixtures oftitanium oxide and one or more sorts of oxide chosen from silicon (Si)and zirconium (Zr) is made into a titanium component; to the powder ofthis titanium component, the water solution that includes the source ofvanadium is added with the organic or inorganic forming assistantgenerally used at this kind of fabrication; then it is heated whilebeing mixed and kneaded to evaporate its moisture and to be pasty to anextent that extrusion is possible; it is fabricated with an extruder inthe shape of a honeycomb etc.; and it is dried and calcined at anelevated temperature (preferably 200-600° C.) in the air.

Moreover, as another method, it is possible to prepare the catalysis byfabricating the titanium component in forms such as a spherical pellet,a cylindrical pellet or a cancellous honeycomb beforehand; calcinatingthe titanium component; and carrying out impregnating support of thewater solution including the source of vanadium. Further, it is possibleto prepare the catalysis by directly kneading the powder of the titaniumcomponent to the powder of vanadium oxide.

Although the catalyst used with the catalyst device 12 is not limited inparticular for BET surface area, it is desirable to be 20-300 m²/g, morepreferably 30-250 m²/g, and the catalyst with such BET surface area ishigh in activity, and excellent in durability. Moreover, when the porevolume by a method of mercury penetration is too small, the catalyticactivity and durability for clearance of the harmful substances of theobject of this invention such as NOx, persistent organic pollutants, avolatile organic compound and CO become low, and when the mercurypenetration is too large, the strength of the catalyst will fall, sothat the pore volume of the catalyst is preferably between 0.3 to 0.55cc/g.

The shape of the above-mentioned oxide catalyst and the noble-metalcatalyst is not limited in particular, and it can be used as apreferable form of the shape of a honeycomb, plainer shape, the shape ofa net, the shape of a column, cylindrical shape and so on.

As for the catalyst temperature of the catalyst device from which thetarget harmful substance is removed, 140° C. or more are desirable, and180° C. or more is more preferable. It is because when the temperatureof the catalyst is less than 140° C., denitration efficiency and thedecomposition efficiency of a volatile organic compound become low.

Although the space velocity of the exhaust gas in the above-mentionedoxide catalyst and the noble-metal catalyst is not restricted inparticular, it is preferably 100-100000 h⁻¹ and more preferably200-50000 h⁻¹. When the space velocity is less than 100 h⁻¹, a devicebecomes large too much, which becomes inefficient, and on the otherhand, when 100000 h⁻¹ is exceeded, there is an inclination for thedenitration efficiency and the decomposition efficiency of a volatileorganic compound to fall.

Although the above-mentioned statement mainly explained the device withthe titanium-vanadium catalyst and plurality of catalysts, if an effectis demonstrated in the exhaust gas treatment concerning this invention,it cannot be limited to the catalyst of a titanium-vanadium but thedevice with one catalyst or more can be used, and it is a matter ofcourse that a service condition is not restricted.

Next, it returns to the explanation of the flow shown in FIG. 1. Thesolid-liquid separator 16 is installed to carry out solid-liquidseparation of the slurry discharged from the wet dust collector 7, and afilter press or the like may be used for it.

The mercury-adsorbing tower 17 is installed to adsorb mercury in thefluid separated with the solid-liquid separator 16. A part of thewastewater W of the mercury-adsorbing tower 17 is supplied to the sodiumhypochlorite generator 9, and it is used to generate sodiumhypochlorite.

Next, the action of the combustion exhaust gas processing device withthe above-mentioned construction will be explained with reference toFIG. 1.

The combustion exhaust gas G1 from the cement kiln 4 desulfurized in thepreheater 2 is introduced into the electrostatic precipitator 6, anddust in the combustion exhaust gas G1 is collected. The combustionexhaust gas G2 which passed the electrostatic precipitator 6 isintroduced into the wet dust collector 7, and the water-solublematerials and dust in the combustion exhaust gas G2 are collected toremove catalyst-poisoning substances which have big effect on the lifeof the latter catalyst device 12, such as dust, sulfuric acid mist,hydrogen chloride (HCl) and mercury (Hg). In this connection, thetemperature of the combustion exhaust gas G2 is controlled to becomeapproximately 100° C.

The slurry generated at the wet dust collector 7 circulates through thecirculating liquid tank 7 a and the pump 8, which allows the contactbetween the combustion exhaust gas G2 and the fluid to be performedsufficiently, and allows the oxidation of mercury and the like by thesodium hypochlorite supplied from the sodium hypochlorite generator 9and the recovery of water-soluble materials and dust to be performedefficiently. In addition, in the wet dust collector 7, while circulatingwater, a part of the water is extracted so as to be supplied to thesolid-liquid separator 16, but this circulating water is discharged tothe grade that does not pose a problem.

The combustion exhaust gas G3 of approximately 80° C. from whichcatalyst-poisoning substances, such as water-soluble materials and dust,are removed, is introduced from the circulating liquid tank 7 a to theheat exchanger 10 and the heater 11, and is heated there. The combustionexhaust gas G3 is heated because it is desirable to perform denitrationof the combustion exhaust gas G4 and decomposition of persistent organicpollutants in the catalyst device 12 at 140-500° C. as mentioned above,and when the decomposition performance and the durability of a catalystare taken into consideration, it is desirable to decompose atapproximately 230-270° C.

The combustion exhaust gas G5 discharged from the catalyst device 12 isused for the heat source of the heat exchanger 10. The heat exchange ofthe combustion exhaust gas G5 discharged from the catalyst device 12 iscarried out with the combustion exhaust gas G3 introduced from the wetdust collector 7 in the heat exchanger 10. Since the temperatureincrease of the combustion exhaust gas G4 cannot fully be performed onlyby the heat exchange in the heat exchanger 10, auxiliary steam ST isintroduced into the heater 11, and the combustion exhaust gas G4 isheated further. The steam with remaining heat or the like in the plantin which the cement burning facility 1 is installed can be used for thisauxiliary steam ST.

Moreover, ammonia (NH₃) as a denitration agent used in the catalystdevice 12 is injected into the entrance side of the heater 11. Theinjection rate of the ammonia is controlled according to the NOxconcentration of the combustion exhaust gas G1 discharged from thepreheater 2. In addition, as stated above, ammonia can be added to aportion between the outlet of the wet dust collector 7 and the inlet ofthe catalyst device 12, where the mixing effect is available other thanthe entrance side of the heater 11. It is possible to add aqueousammonia to the combustion exhaust gas after preheating with the heater11 and to allow the gas to pass the catalyst device 12.

Next, the combustion exhaust gas G4 is supplied to the catalyst device12, and NOx, persistent organic pollutants, a volatile organic compound,CO, etc. are removed through decomposition and so on. As mentionedabove, the temperature in the catalyst device 12 is controlled at140-500° C. preferably 230-270° C. which is suitable for denitration ofcombustion exhaust gas G and decomposition of persistent organicpollutants. Here, since the heat exchanger 10 is arranged, it ispossible to control the temperature in the catalyst device 12 highly,and raising the operating temperature of the catalyst device 12 as muchas possible allows the efficiency of the catalyst device 12 to rise,which can reduce the amount of the catalyst.

The combustion exhaust gas G5 from the catalyst device 12 is emitted tothe air through the heat exchanger 10, the fan 14 and the stack 15. Thetemperature of the combustion exhaust gas G6 becomes approximately 110°C. due to the recovery of its remaining heat.

Meanwhile, the slurry S discharged from the circulating liquid tank 7 ais solid-liquid separated by the solid-liquid separator 16, and the cakeC separated is used as a cement raw material. On the other hand, mercuryin the fluid separated by the solid-liquid separator 16 dissolves inwater as a chloro-complex ion (HgCl₄ ²⁻), and this ion is adsorbed bythe mercury-adsorbing tower 17. As to the mercury, it is possible tosolid-separate as (HgCl₂), and then ion may be adsorbed and separated.Some wastewater W from which mercury is removed is supplied to thesodium hypochlorite generator 9, others can be processed out of thesystem or it can also use them for the cooling of the combustion exhaustgas G1 of the cement kiln 4, a water spray of a cement raw material millor a dryer for a cement raw material and so on.

Embodiment 1

Next, as the first embodiment of the device and method for processingcement kiln combustion exhaust gas according to the present invention,each harmful-substance-elimination factor, using thecombustion-exhaust-gas processing device with the construction shown inFIG. 1 and a titanium-vanadium catalyst for the catalyst device 12, isshown in Table 1. In this test, the combustion-exhaust-gas temperatureat the inlet of the catalyst device 12 was 180° C., and space velocity(SV value) was set to be 5060 h⁻¹. In addition, theharmful-substance-elimination factor is computed using the concentrationof each harmful substance of the outlet of the electrostaticprecipitator 6, and the concentration of each harmful substance of theoutlet of the catalyst device 12. That is, the rate that the catalystdevice 12 removes each harmful substance in the outlet of theelectrostatic precipitator 6 is shown.

TABLE 1 Harmful Elimination substances factor (%) Nox 97 Persistentorganic 86 pollutants Mercury (Hg) 97 Smoke dust 90 Ammonia (NH3) 84Odor 90 PCB 92

As shown in Table 1, it is possible to efficiently remove harmfulsubstances, such as NOx, persistent organic pollutants, a volatileorganic compound, dust, and PCB, by this invention.

Embodiment 2

Next, as the second embodiment of the device and method for processingcement kiln combustion exhaust gas according to the present invention,each harmful-substance-elimination factor, using thecombustion-exhaust-gas processing device with the construction shown inFIG. 1 and at the time of arranging a titanium-vanadium catalyst (oxidecatalyst) upstream, and platinum catalyst (noble-metal catalyst)downstream at the catalyst device 12, is shown in Table 2.

This test was carried out under the condition that thecombustion-exhaust-gas temperature at the inlet of the catalyst device12 was 180° C., 210° C. and 250° C. Moreover, space velocity (SV value)was set to be 5,060 h⁻¹ by the titanium-vanadium catalyst, and 24,200h⁻¹ by the platinum catalyst. The reducing agent (NH₃ gas) was sprayedupstream of the catalyst device, and the mole ratio of NOx and NH₃ wasset to be 1. In this connection, the harmful-substance-eliminationfactor is computed using each harmful substance concentration of theoutlet of the electrostatic precipitator 6, and the concentration ofeach harmful substance of the outlet of the catalyst device 12. That is,the rate that the catalyst device 12 removed each harmful substance inthe outlet of the electrostatic precipitator 6 is shown.

Further, as a comparative example 1, the form, which has arranged theplatinum catalyst upstream, and has arranged the titanium-vanadiumcatalyst downstream at the catalyst device 12, under the same otherconditions as the Embodiment 2, was tested.

TABLE 2 Embodiment 2 Comparative example 1 Gas temperature 180° C. 210°C. 250° C. 180° C. 210° C. 250° C. Harmful Eliminaition factor (%)Eliminaition factor (%) substances Nox 97 98 99 97 75 20 Persistent 8992 93 89 92 93 organic pollutants Mercury (Hg) 97 97 97 97 97 97 Smokedust 90 90 90 90 90 90 Ammonia 97 98 99 97 98 99 (NH3) Odor 95 98 99 9585 70 PCB 95 98 99 95 98 99 CO 98 99 99 98 99 99 Embodiment 2→Upstream:Oxidation catalyst, Downstream: Noble-metal catalyst Comparative example1→Upstream: Noble-metal catalyst, Downstream: Oxidation catalyst

As shown in Table 2, by using a platinum catalyst together, most COs isremovable while being able to raise the elimination factor of ammoniafurther. However, it is more desirable to install an oxide catalystupstream and to install a noble-metal catalyst downstream like theEmbodiment 2 of this invention, since the elimination factor falls alsoabout an odor in the comparative example 1 while the elimination factorof NOx falls substantially when the combustion-exhaust-gas temperatureof the inlet of the catalyst device 12 is 250° C.

As mentioned above, as an arrangement form of the catalyst of thecatalyst device 12, independently installed oxide catalyst in theupstream is preferably effective. Moreover, further excellent effect isacquired by making it the two steps of catalyst system with upstreamoxide catalyst and downstream noble-metal catalyst, and it is still moredesirable.

In an oxide independent system, the decomposition clearance of NOx, avolatile organic compound, and persistent organic pollutants, which arethe harmful substances in exhaust gas, is attained. Moreover, when theupstream is equipped with an oxide catalyst, the downstream is equippedwith a noble-metal catalyst to form a two-step catalyst system, thedecomposition clearance of NOx, a volatile organic compound, andpersistent organic pollutants, which are the harmful substances inexhaust gas, is attained; the decomposition clearance of CO is attainedsimultaneously; and the decomposition performance of the volatileorganic compound is also improved, resulting in further excellenteffect.

Further, although it becomes possible to carry out decompositionclearance of the NOx by spraying ammonia gas in the process in which NOxis removed with an upper catalyst, in case that ammonia without reactionremains at the upstream catalyst and it emits to the air as it is, itmay become the origin of a secondary environmental pollution. In orderto prevent this, in ammonia injection control, it is necessary toperform close control to avoid the problem. In this connection, withtwo-step catalyst system that equipped with an upstream oxide catalystand a downstream noble-metal catalyst, the downstream catalyst attainsdecomposition clearance of ammonia without reaction; precise control isunnecessary; and the secondary environmental pollution by ammonia can besuppressed.

Embodiment 3

Next, as the third embodiment of the device and method for processingcement kiln combustion exhaust gas according to the present invention,each harmful-substance-elimination factor, using thecombustion-exhaust-gas processing device with the construction shown inFIG. 1 and the time of arranging a titanium-vanadium catalyst (oxidecatalyst) upstream, and platinum catalyst (noble-metal catalyst)downstream at the catalyst device 12, is shown in Table 3.

In this test, the temperature of combustion exhaust gas at the inlet ofthe catalyst device 12 was 180° C. Space velocity (SV value) was set tobe 5,060 h⁻¹ for the titanium-vanadium catalyst, and 24,200 h⁻¹ for theplatinum catalyst. As for the mesh size (bore diameter) of the catalyst,a 2.9 mm honeycomb catalyst for the titanium-vanadium catalyst was usedand a 1.77 mm honeycomb catalyst for the platinum catalyst. The reducingagent (NH₃ gas) was sprayed upstream of the catalyst device, and set themole ratio of NOx and NH₃ was set to be 1. In this connection, the meshsize (bore diameter) of a catalyst means, as shown in FIG. 3, thedimension L from the left end to the right end of the hole (a squareshape) 12 a through which the exhaust gas of the honeycomb-like catalyst12 passes. Moreover, to the wet dust collector 7 in FIG. 1, sodiumhypochlorite of which concentration was 2 mg/kg-H₂O was added. Theelimination factor and durability of each harmful substance are shown inTable 3.

Further, as a comparative example 2, the process shown in FIG. 1 withoutwet dust collector under the same conditions of the arrangement, themesh size of catalyst and others as the Embodiment 3, was tested.

TABLE 3 Initial elimination 1000 hours after elimination Harmfulsubstances factor (%) factor (%) Embodiment 3 Nox 97 96 Persistentorganic 89 89 pollutants Mercury (Hg) 97 97 Smoke dust 90 90 Ammonia(NH3) 97 96 Odor 95 95 PCB 95 95 CO 98 96 Comparative example 2 NOX 9790 Persistent organic 89 82 pollutants Mercury (Hg) 0 0 Smoke dust 0 0Ammonia (NH3) 97 90 Odor 95 70 PCB 95 88 CO 98 70

As clearly shown in the table, by the comparative example 2, althoughmercury and smoke dust cannot be removed, and the initial eliminationfactor is the same as that of Embodiment 3 also about other harmfulsubstances, the elimination factor after 1000 hours falls fromEmbodiment 3, and it turns out that it is inferior in durability.

In addition, in the above-mentioned embodiment, although the wet dustcollector 7 which adds sodium hypochlorite to the combustion exhaust gasG2 was used as a catalyst-poisoning-substance stripper, a bag filter forwhich dust is collected while blowing activated carbon into thecombustion exhaust gas G2 can also be used. With the activated carbon,dust, mercury and SOx are efficiently removable.

EXPLANATION OF REFERENCE NUMBERS

-   -   1 cement burning facility    -   2 preheater    -   3 calciner    -   4 cement kiln    -   5 clinker cooler    -   6 electrostatic precipitator    -   7 wet dust collector    -   7 a circulating liquid tank    -   8 pump    -   9 sodium hypochlorite generator    -   8 heat exchanger    -   11 heater    -   12 catalyst device    -   12 a hole through which exhaust gas passes    -   14 fan    -   15 stack    -   16 solid-liquid separator    -   17 mercury adsorbing tower

This disclosure provides exemplary embodiments of the present invention.The scope of the present invention is not limited by these exemplaryembodiments. Numerous variations, whether explicitly provided for by thespecification or implied by the specification, such as variations instructure, dimension, type of material and manufacturing process, may beimplemented by one skilled in the art in view of this disclosure.

1. A device for processing cement kiln combustion exhaust gascomprising: a dust collector configured to collect dust in cement kilncombustion exhaust gas; a catalyst-poisoning-substance stripperconfigured to remove a catalyst-poisoning substance and mercury from thecement kiln combustion exhaust gas that passed said dust collector byadding sodium hypochlorite to said cement kiln combustion exhaust gas; apreheater configured to heat beforehand the cement kiln combustionexhaust gas that passed said catalyst-poisoning-substance stripper; acatalyst device configured to remove at least one member selected fromthe group consisting of a volatile organic compound, carbon monoxide, apersistent organic pollutant, hydrocarbon and an offensive odorsubstance in the cement kiln combustion exhaust gas preheated by saidpreheater; and a mercury adsorbing tower which adsorbs mercury in fluidexhausted from the catalyst-poisoning substance stripper, the mercuryadsorbing tower producing wastewater, wherein a portion of thewastewater is used to generate sodium hypochlorite.
 2. The device forprocessing cement kiln combustion exhaust gas as claimed in claim 1,wherein nitrogen oxide in the cement kiln combustion exhaust gaspreheated by the preheater is removed together with at least one avolatile organic compound, carbon monoxide, a persistent organicpollutant, hydrocarbon and an offensive odor substance.
 3. The devicefor processing cement kiln combustion exhaust gas as claimed in claim 1,wherein said catalyst-poisoning-substance stripper is a wet dustcollector that removes the catalyst-poisoning substance from the cementkiln combustion exhaust gas.
 4. (canceled)
 5. The device for processingcement kiln combustion exhaust gas as claimed in claim 1, whereinconcentration of said sodium hypochlorite is in a range of 1 mg/L or inmore and 1,000 mg/L or less.
 6. The device for processing cement kilncombustion exhaust gas as claimed in claim 1, wherein said catalystdevice is provided with an oxide catalyst installed in an upstream sideand a noble-metal catalyst installed in a downstream side.
 7. The devicefor processing cement kiln combustion exhaust gas as claimed in claim 6,wherein a reducing agent is sprayed from an entrance-side upper part ofsaid catalyst device.
 8. The device for processing cement kilncombustion exhaust gas as claimed in claim 6, wherein said oxidecatalyst is a titanium-vanadium catalyst.
 9. The device for processingcement kiln combustion exhaust gas as claimed in claim 6, wherein saidnoble-metal catalyst is a catalyst having at least one noble metalselected from platinum, palladium, rhodium and ruthenium.
 10. The devicefor processing cement kiln combustion exhaust gas as claimed in claim 9,wherein a mesh size (bore diameter) of said catalyst is in a range of1.75 mm or more and 3.75 mm or less.
 11. The device for processingcement kiln combustion exhaust gas as claimed in claim 1, wherein saidpreheater is a Ljungstrom-type heat exchanger, a heat pump or a heatpipe.
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled) 16.The device for processing cement kiln combustion exhaust gas as claimedin claim 8, wherein a mesh size (bore diameter) of said catalyst is in arange of 1.75 mm or more and 3.75 mm or less.
 17. The device forprocessing cement kiln combustion exhaust gas as claimed in claim 1,further comprising a solid-liquid separator in fluid communication withthe catalyst-poisoning-substance stripper and configured to separatedischarge of the catalyst-poisoning-substance stripper into solid andliquid components, the liquid component being fed to the mercuryabsorbing tower.
 18. The device for processing cement kiln combustionexhaust gas as claimed in claim 17, further comprising a sodiumhypochlorite generator in fluid communication with thecatalyst-poisoning-substance stripper and the mercury absorbing tower,the sodium hypochlorite generator being configured to use the wastewaterfrom the mercury adsorbing tower to generate sodium hypochlorite andsupply sodium hypochlorite to the catalyst-poisoning-substance stripper.